The recent era of digital dentistry has had a significant impact on the restorative methods used for conventional and implant dentistry. Technologies such as digital data acquisition, computer aided design (CAD), computer aided manufacturing (CAM) now exist that enable the clinician and laboratory to develop highly aesthetic patient-specific restorations. Traditionally, stock dental components (or a hand modified version of such components) were adapted to specific patients. Such traditional methods depended on manual measurement and tooling, and as a result were time consuming and suffered from accuracy issues. The traditional methods of manual measurement and tooling of a component are being replaced by virtually designed restorations based on digitally acquired anatomic datasets.
An example of computer aided design and manufacture of a customized dental component may be the dental restoration of a partially or wholly edentulous patient with artificial dentition. An incision is made through the gingiva to expose the underlying bone. An artificial tooth root, usually a dental implant, is placed in the jawbone for integration. The dental implant generally includes a threaded bore to receive a retaining screw holding mating components therein. During the first stage, the gum tissue overlying the implant is sutured and heals as the osseointegration process continues.
Once the osseointegration process is complete, the gum tissue is re-opened to expose the end of the dental implant. A healing component or healing abutment is fastened to the exposed end of the dental implant to allow the gum tissue to heal therearound. Preferably, the gum tissue heals such that the aperture that remains generally approximates the size and contour of the aperture that existed around the natural tooth that is being replaced. To accomplish this, the healing abutment attached to the exposed end of the dental implant has the same shape as the gingival portion of the natural tooth being replaced. The healing abutment is removed and an impression coping is fitted onto the exposed end of the implant. This allows an impression of the specific region of the patient's mouth to be taken so that an artificial tooth is accurately constructed. Thus, in typical dental implant systems, the healing component and the impression coping are two physically separate components. Preferably, the impression coping has the same gingival dimensions as the healing component so that there is no gap between the impression coping and the wall of the gum tissue defining the aperture. Otherwise, a less than accurate impression of the condition of the patient's mouth is made. The impression coping may be a “pick-up” type impression coping or a “transfer” type impression coping, both known in the art. After these processes, a dental laboratory creates a prosthesis to be permanently secured to the dental implant from the impression that was made.
In addition to the method that uses the impression material and mold to manually develop a prosthesis, systems exist that utilize scanning technology to assist in accurately generating a prosthesis. A scanning device is used in one of at least three different approaches. First, a scanning device can scan the region in the patient's mouth where the prosthesis is to be placed without the need to use impression materials or to construct a mold. Second, the impression material that is removed from the healing abutment and surrounding area is scanned. Third, a dentist or technician can scan the stone model of the dental region that was formed from the impression material and mold to produce the permanent components.
Three basic scanning techniques exist, laser scanning, photographic imaging and mechanical sensing. Each scanning technique is used or modified for any of the above-listed approaches (a scan of the stone model, a scan of the impression material, or a scan in the mouth without using impression material) to create the prosthesis. After scanning, a laboratory can create and manufacture the permanent crown or bridge, usually using a computer aided design (CAD) package.
The utilization of a CAD program is one method of creating a three dimensional model based on scanning a dental region. Preferably, after the impression is made of the patient's mouth, the impression material or stone model is placed on a support table defining the X-Y plane. A scanning laser light probe is directed onto the model. The laser light probe emits a pulse of laser light that is reflected by the model. A detector receives light scattered from the impact of the beam with the impression to calculate a Z-axis measurement. The model and the beam are relatively translated within the X-Y plane to gather a plurality of contact points with known location in the X-Y coordinate plane. The locations of several contact points in the Z-plane are determined by detecting reflected light. Finally, correlating data of the X-Y coordinates and the Z-direction contact points creates a digital image. Once a pass is complete, the model may be tilted to raise one side of the mold relative to the opposite vertically away from the X-Y plane. Subsequent to the model's second scan, the model may be further rotated to allow for a more accurate reading of the model. After all scans are complete, the data may be fed into a CAD system for manipulation of this electronic data by known CAD software.
Photographic imaging can also used to scan impression material, a stone model or to scan directly in the mouth. For example, one system takes photographs at multiple angles in one exposure to scan a dental region, create a model and manufacture a prosthetic tooth. This process is generally initiated with the process of taking a stereophotograph with a camera from approximately 50 to 150 mm away from the patient's mouth. The stereophotograph can involve a photograph of a patient's mouth already prepared with implantation devices. Correct spatial positioning of the dental implants is obtained by marking the implant in several locations. The resulting photograph presents multiple images of the same object. The images on the photographs are scanned with a reading device that digitizes the photographs to produce a digital image of the dental region. The data from the scanner is electronically transmitted to a graphical imaging program that creates a model that is displayed to the user. After identification of the shape, position and other details of the model, the ultimate step is the transmission of the data to a computer for manufacturing.
The third scanning technique uses mechanical sensing. A mechanical contour sensing device is used to read a dental model and produce a prosthetic tooth. The impression model is secured to a table that may rotate about its longitudinal axis as well as translate along the same axis with variable speeds. A mechanical sensing unit is placed in contact with the model at a known angle and the sensing equipment is held firmly against the surface of the model by a spring. When the model is rotated and translated, the sensing equipment can measure the changes in the contour and create an electronic representation of the data. A computer then processes the electronic representation and the data from the scanning device to create a data array. The computer then compresses the data for storage and/or transmission to the milling equipment.
While the current technologies provide a means by which to design and manufacture improved prosthetic restorations, the scope is limited to macro geometry, material type and color shade inputs. A post-processing step is therefore required to create a desirable surface finish (or a multitude of surface finishes) for a restoration component to facilitate needs such as aesthetics, plaque resistance, soft tissue preservation, and restorative retention. Adding to the complexity, this additional step of surface finish selection is open to artistic interpretation of the customer and needs/inputs by the dental laboratory and is limited by the fabrication techniques employed (typically hand manipulation). Thus, while the surface finishes can be modified subsequent to the component fabrication, this is restricted by (a) the ability of the customer to clearly communicate their needs and (b) the skill of the technician in being able to recreate the associated input(s) when fabricating the desired component.
As with the macro geometrical design, there is a need to predictably control (specify and produce) the surface finish so that the desired end state for a particular component is achieved. There is also a need to provide an accessible interface for a designer to designate finishes that may be accurately implemented by a tooling system to produce the desired finishes for the component surfaces. There is a further need for a visual interface allowing a designer to accurately designate finishes for the surfaces of a computer generated component.